The present invention relates generally to the field of vehicle seating, more specifically, vehicle seat frame assemblies with front and rear tilting capabilities as well as a method for manufacturing the same.
Vehicle seat frame assemblies typically include a seat (having a seat bottom or cushion and a seat back) and may include seat adjusters that alter the position of the seat frame. Seat adjusters are used for many purposes, such as on a captain's seat to provide selective horizontal fore and aft movement of the seat, vertical movement of the seat, and/or pivotal movement of the seat back, as is well known. The ability to adjust the position of the seat is desirable to enable vehicle occupants of various sizes to be comfortably and properly seated within the vehicle.
Vehicle seat brackets and tracks include adjuster systems for frontward/rearward tilting of the seat cushion frame. Such features may be manually or automatically operable. The seat track includes a torque (or torsion) tube extending between side brackets (or “B-brackets”) of the seat frame. The torsion tube includes a shank portion located between the side brackets and typically subjacent the cushion on the seat bottom. The torsion tube includes a head portion at each end coupled to a side bracket on each side of the seat frame along with a bell crank or pivot linkage. The pivot linkage is coupled to the horizontal adjustment rails or a floor bracket mounted thereto. An actuator selectively rotates the pivot linkages. For example, in some arrangements, rotation of the front pivot linkages in one direction moves the front portion of the seat upward; rotation of the rear pivot linkages in the opposite direction moves the rear portion of the seat upward with respect to the vehicle floor. Some automatic seat adjuster systems utilize a powered drive mechanism (typically an electric motor) in conjunction with a system of gears and other components to adjust the seat cushion. For example, it is known to use a motor-driven threaded screw attached to the pivot linkage to selectively lift and lower the seat cushion.
It is further known to have the torsion tube coupled to the side bracket through a swaging process employing a ram forming technique commonly referred to as “column loading” in the axial direction of the tube. A mandrel or die is forced into the head portion of the torsion tube at a predetermined pressure level to reduce clearances between the side bracket and the torsion tube. The die defines an outer diameter that is smaller at the front end than the rearward portion of the die. The die forces the end of the head portion of the torsion tube to flare outward, thereby radially and axially restricting the side bracket from moving beyond the head portion of the torsion tube. However, this process can be imprecise as it is difficult to control the extent of flaring and depth of axial deformation resulting from column loading. It is also know to utilize a Belleville washer, or other axially adjustable washer or device, to accommodate the variable axial clearance (or lateral looseness) between the flared portion of the tube and the side bracket. However, Belleville washers increase the overall cost and complexity of the vehicle seat frame assembly.
The integrity of the fit between the side bracket and the torsion tube influences user comfort, seat stability, BSR (buzz-squeak-rattle) values and longevity. A loose fitting between the side bracket and torsion tube can lead to deflection in the other parts of the seat assembly. For example, one original equipment manufacturing test involves measuring the deflection of the seat back with respect to the vehicle floor during simulated normal highway driving conditions. Excessive deflection of the seat back is indicative of a vehicle seat assembly having lower “stability values.” When the connection between the torsion tube and the side bracket has substantial axial and/or radial spacing between each element, the seat stability values are high (indicating high deflection in the seat frame assembly) and the user may experience more vibration in the seat back and other portions of the seat.
To improve the connection of the side bracket and torsion tube some seat manufacturing techniques use multiple iterations of axial or column loading. Multiple iterations may reduce deflection of the seat back and increase the stability of the seat assembly. However, such additional steps increase manufacturing time and costs of the vehicle seat frame. Moreover, column loading may produce less precise results and yield more broadly ranging deflection values (e.g. SCL1, charting the stability values for a seat after one iteration of axial loading, and SCL2, charting the stability values for a seat after multiple iterations of axial loading, as shown in FIG. 1).
One drawback of multiple iteration column loading is that when simultaneously performed on each side of the torsion tube, the mid-section of the torsion tube undergoes compressive stresses which cause the tube to deform or possibly buckle. Such deformation may cause the tube to exceed predetermined dimensional tolerances.
One alternative arrangement utilizes arc welding to affix a torsion tube to the side brackets and incorporates a rotatable insert in the torsion tube. However, welding can alter the strength of the workpiece and this design is costly due to processing times and additional part requirements.
It remains desirable to provide a vehicle seat frame assembly having a seat cushion adjusting feature with a torsion tube coupled to the seat frame utilizing more cost efficient manufacturing techniques which provide greater design and manufacturing flexibility while providing increased seat stability and durability.